Organic light-emitting diode (OLED) devices, also referred to as organic electro-luminescent (EL) devices, have numerous well-known advantages over other flat-panel display devices currently in the market place. Among these advantages are brightness of light emission, relatively wide viewing angle, and reduced electrical power consumption compared to, for example, liquid crystal displays (LCDs) using back-lighting.
Applications of OLED devices include active-matrix image displays, passive-matrix image displays, and area lighting devices such as, for example, selective desktop lighting. Irrespective of the particular OLED device configuration tailored to these broad fields of applications, all OLED devices function on the same general principles. An organic electro-luminescent (EL) medium structure is sandwiched between two electrodes. At least one of the electrodes is light transmissive. These electrodes are commonly referred to as an anode and a cathode in analogy to the terminals of a conventional diode. When an electrical potential is applied between the electrodes so that the anode is connected to the positive terminal of a voltage source and the cathode is connected to the negative terminal, the OLED is said to be forward-biased. Positive charge carriers (holes) are injected from the anode into the EL medium structure, and negative charge carriers (electrons) are injected from the cathode. Such charge carrier injection causes current flow from the electrodes through the EL medium structure. Recombination of holes and electrons within a zone of the EL medium structure results in emission of light from this zone that is, appropriately called, the light-emitting zone or interface. The emitted light is directed towards an observer, or towards an object to be illuminated, through the light transmissive electrode. If the light transmissive electrode is between the substrate and the light emissive elements of the OLED device, the device is called a bottom-emitting OLED device. Conversely, if the light transmissive electrode is not between the substrate and the light emissive elements, the device is referred to as a top-emitting OLED device.
The organic EL medium structure can be formed of a stack of sub-layers that can include small molecule layers and polymer layers. Such organic layers and sub-layers are well known and understood by those skilled in the OLED art.
Because light is emitted through an electrode, it is important that the electrode through which light is emitted be sufficiently light transmissive to avoid absorbing the emitted light. Typical prior-art materials used for such electrodes include indium tin oxide and very thin layers of metal. However, the current carrying capacity of electrodes formed from these materials is limited, thereby limiting the amount of light that can be emitted from the organic layers.
In top-emitting OLED devices, light is emitted through an upper electrode or top electrode which has to be sufficiently light transmissive, while the lower electrode(s) or bottom electrode(s) can be made of relatively thick and electrically conductive metal compositions which can be optically opaque.
In conventional integrated circuits, bus connections are provided over the substrate to provide power to circuitry in the integrated circuit. These busses are located directly on the substrate or on layers deposited on the substrate, for example on planarization layers. In complex circuits, multiple levels of bus lines are located over the substrate and separated by insulating layers of material. For example, OLED displays such as the AM550L sold by the Eastman Kodak Company utilize multiple bus lines located on the substrate and on various planarization layers. However, these busses are not useful to provide power to the light transmissive upper electrode in an OLED device because conventional photolithography techniques destroy the organic layers and thin upper electrode necessary for a top-emitting OLED device.
Co-pending, commonly assigned U.S. Publication No. 2004/0253756, published Dec. 16, 2004 entitled “Method Of Making A Top-Emitting OLED Device Having Improved Power Distribution” proposes to solve this problem by employing a method of making a top-emitting OLED device that includes providing over a substrate laterally spaced and optically opaque lower electrodes and upper electrode busses which are electrically insulated from the lower electrodes; depositing an organic EL medium structure over the lower electrodes and the upper electrode busses; selectively removing the organic EL medium structure over at least portions of the upper electrode busses to reveal at least upper surfaces of the upper electrode busses; and depositing a light transmissive upper electrode over the organic EL medium structure so that such upper electrode is in electrical contact with at least upper surfaces of the upper electrode busses. This method will effectively provide power to the upper electrode. However, the selectively removed organic EL material may re-deposit in other areas of the EL medium structure.
There are means known in the art to avoid the re-deposition of removed or ablated material. For example, US Publication 2004/0051446 A1 entitled “Method And Apparatus For Structuring Electrodes For Organic Light-Emitting Display And Organic Light-Emitting Display Manufactured Using The Method And Apparatus” published Mar. 18, 2004 describes a method for structuring an electrode, such as, for example, a cathode and/or an anode, for an organic light-emitting display by ablating the electrodes using a laser beam. An apparatus using the method for structuring an electrode is also provided. The laser beam is expanded to cover at least one target portion of each electrode to be ablated. A method for repairing an organic light-emitting display using the method and apparatus is also provided. In some embodiments, the invention employs an exhaust unit and outlet vent. However, as described, the method is relatively slow, employing only one laser beam and the risk of re-deposition of ablated material is high since only a single exhaust unit may be employed and at some distance from the point of ablation.
W09903157 entitled “Laser Ablation Method To Fabricate Color Organic Light Emitting Diode Displays” published 1999 Jan. 21 describes another ablation method using lasers. In this disclosure laser radiation may be used to ablate organic materials as well as metals. A method of using such laser ablation to selectively remove organic material and metal material from an organic light emitting device (OLED) work piece is also disclosed. The ablation enables fabrication of multi-color pixels in OLED displays. A novel OLED structure having adjacent multi-colored organic stakes is disclosed. Further, a novel ablation chamber in which an OLED structure may be subjected to laser ablation is also disclosed. The ablation chamber includes means for moving an OLED structure within the chamber, means for detecting an ablation endpoint, and means for suctioning ablated material from the chamber. Although a plurality of suction mechanisms are referenced in this disclosure, as illustrated, the suction mechanisms also have a significant risk of re-deposition of ablated material. Moreover, the ablation process will be relatively slow.
In an alternative approach to debris removal, U.S. Pat. No. 6,683,277 B1 and U.S. Pat. No. 6,797,919 B1 both entitled “Laser Ablation Nozzle Assembly” and issued Jan. 27, 2004 and Sep. 28, 2004 respectively, describe laser ablation systems including a first embodiment of a nozzle assembly where a laser beam is emitted through the nozzle assembly to remove materials on a target. The nozzle assembly includes a nozzle having a top end, and a window placed on the top end of the nozzle. The window includes one or more apertures and the laser beam is emitted through one of those apertures. Another laser ablation system includes a second embodiment of a nozzle assembly where a laser beam is emitted through the nozzle assembly to remove materials on a target. The nozzle assembly includes a nozzle having one or more channels at a top end of the nozzle. The nozzle assembly also includes a window that is placed on the one or more channels. A gas flows through the one or more channels and that gas flow reduces debris deposition on the window. Yet another laser ablation system includes a third embodiment of a nozzle assembly that includes a nozzle that has a central channel aligned longitudinally through which said laser beam travels from a top end of said nozzle to a bottom end of said nozzle. In this embodiment, the central channel of the nozzle is threaded. These designs for removing debris in a laser ablation system limit can clog easily and are limited in their throughput. Debris can deposit in the apertures, impeding the propagation of the laser light to a target.
There is a need, therefore for an improved method and apparatus for selectively removing material from a surface at an improved rate and with reduced contamination.